On Tue, Jan 25, 2022 at 03:55:31AM +0000, Tian, Kevin wrote: > > From: Jason Gunthorpe <jgg@xxxxxxxxxx> > > Sent: Saturday, January 15, 2022 3:35 AM > > + * > > + * The peer to peer (P2P) quiescent state is intended to be a quiescent > > + * state for the device for the purposes of managing multiple devices > > within > > + * a user context where peer-to-peer DMA between devices may be active. > > The > > + * PRE_COPY_P2P and RUNNING_P2P states must prevent the device from > > + * initiating any new P2P DMA transactions. If the device can identify P2P > > + * transactions then it can stop only P2P DMA, otherwise it must stop all > > + * DMA. The migration driver must complete any such outstanding > > operations > > + * prior to completing the FSM arc into either P2P state. > > + * > > Now NDMA is renamed to P2P... but we did discuss the potential > usage of using this state on devices which cannot stop DMA quickly > thus needs to drain pending page requests which further requires > running vCPUs if the fault is on guest I/O page table. I think this needs to be fleshed out more before we can add it, ideally along with a driver and some qemu implementation It looks like the qemu part for this will not be so easy.. Jason
